Going to bed too early may wreak havoc on metabolics

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Note that this study was published as an abstract and presented at a conference. These data and conclusions should be considered to be preliminary until published in a peer-reviewed journal.

People who altered their normal sleep patterns in order to get up early for school or work may have upset their natural circadian rhythms, which seemed to have an impact on their eating habits.

Note that subjective sleep quality and sleep duration were not correlated with phase angle (a measure of melatonin onset), and their was no overall correlation with body mass index or overall body fat.

SEATTLE -- People who altered their normal sleep patterns in order to get up early for school or work may have upset their natural circadian rhythms, which seemed to have an impact on their eating habits, researchers reported here.

Study participants with a shortened phase angle associated with dim light melatonin onset -- that is, they went to sleep before the normal time of melatonin release -- ingested an average of 369 calories more compared with others with a longer phase angle (P=0.027), said Kelly Baron, PhD, MPH, of the Feinberg School of Medicine at Northwestern University in Chicago, and colleagues.

They also found that participants with short phase angle ate more carbohydrates (P=0.013) and ate meals more frequently (P=0.02), according to their report at the Associated Professional Sleep Societies meeting.

However, subjective sleep quality and sleep duration were not correlated with phase angle, and their was no overall correlation with body mass index (BMI) or overall body fat, they added. They did observe that phase angle was inversely associated with body fat in men (P=0.04).

Baron said the study was one of the first to show the relationships between sleep and metabolics. She pointed out that going to bed too early may prove as problematic as going too late.

"The use of this information could be leading us toward precision medicine and understanding what is the right schedule for your body and getting your body on the right schedule," she said.

But she cautioned that "these measures of sleep are not yet ready for prime time in the clinic. Í think that as we learn more about these measures, we may be able to use it in the clinic."

In commenting on the study, David Rapoport, MD, professor of medicine at the New York University Langone Medical Center in New York City, told MedPage Today that "looking at the relationship of sleep as a driver of metabolic activity is a very popular area of investigation. People have looked at it in a variety of different ways. They are looking at phasing of sleep rather than integrity and duration of sleep. It makes perfect sense that metabolism and sleep are regulated by the same areas of the brain."

Rapoport said he agreed with Baron that more study is needed before the results can be translated into treatment, but he added that "these findings are relevant to the obesity epidemic."

Using telephone and web-based interviews, Baron's group recruited 97 nonshift workers, ages 18 to 50 (mean age 26.7), who reported good sleep quality and got more than 6.5 hours of sleep a night. More than half of the participants were women (61) and 36 were men. A little over 60% self-identified as white. About 40% of the group were students; 80% were either students or were working.

The group's mean BMI was 24 kg/m2 and their mean body fat was 30.4%.

"While the average body mass index was in the normal range, about one-third ... were either overweight or obese," Baron pointed out.

The average bedtime for the participants was 11 p.m., which is later that the general population, Baron explained, but not surprising because many in the group described themselves as "night owls." The average dim light melatonin onset was 2.1 hours, she said.

Baron explained that people produce melatonin starting 2 hours before bedtime. But people who are used to getting up at 8 a.m. on weekends will get up at 6 a.m. on work days, so they go to sleep earlier, shortening the normal phase angle, she said.

The participants went through a 7-day period for completing questionnaires and recording sleep and activities with actigraphy, which confirmed a 6.5-hour sleep period. They completed food diaries in the 7 days before spending one night in the clinical research unit. They had blood draws taken to determine melatonin levels. In addition, they were weighed each morning and their height was measured to determine BMI. Body fat was measured using dual emission x-ray absorptiometry.

Baron's group reported that the timing of sleep appeared to influence food intake behaviors, such as eating fast food and lower level of fruits and vegetables, as well as other health behaviors (alcohol consumption, smoking habits, sedentary lifestyles. More recently, sleep timing has been linked to obesity, diabetes, and the risk for metabolic syndrome.

As a limitation, Baron noted that the study population consisted of healthy adults who did not have metabolic abnormalities.

But the results indicate that "circadian misalignment in everyday life may impact risk for obesity," her group wrote.

Baron disclosed no relevant relationships with industry.

Rapoport disclosed no relevant relationships with industry.

Reviewed by Robert Jasmer, MD Associate Clinical Professor of Medicine, University of California, San Francisco

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